Brisbane Valley Storms
Monday December 26, 2005chase report
I had never thought of chasing on this day, but when I was freed of some morning commitments, I thought it was worth a shot. Instability continued to be moderate with the potential for severe pulse storms in the sultry conditions and light shear. The previous day's storms (I couldn't chase them!) were some of the most lightning active I've seen in years, and I was hoping for something at least half as good. Just before I left, surface charts revealed a north-south line of convergence just west of Gatton, so that's where I headed.
Not long out of Brisbane, it was good to see cumulus congestus appear through the haze along the convergence. Closer to Gatton, it appeared that much of the congestus was having a tough time getting close to breaking the cap, and when I spotted a better updraft (though of 'turkey variety') to the NW, I made the decision to take the road northwards to Esk.
By the time I reached Esk, the updrafts had struggled to put out a weak anvil, but I continued on, and as I neared Blackbutt, a much stronger updraft shot up, and soon this became the first thunderstorm of the day over Yarraman.
I stopped with a good view of the storm near Blackbutt, to the sound of near-constant thunder and 36C temperatures. The storm was slowly organising, and soon its rain curtain thickened nicely, with white traces hinting at hail.
CG lightning was becoming more frequent, especially on the western side of the multicell storm. After a little while, I decided the storm wasn't too nasty, so I punched through the rain curtain to get in front of it. As I reached the front edge of the still developing storm, the moderate rain became quite heavy, and winds started to gust up to about 30kn. I then reached Nanango which was just north of the storm, and I waited in town to get some video of the storm moving over. A gust front slowly moved towards town accompanied by winds nearing gale force, heavy rain, and after a while, pea sized hail. Towards the end of the storm, the hail became a bit more intense, with larger thuds on the roof, suggesting some stones into the severe range (2cm+), but overall it was a relatively gentle storm compared to others during the season.
The sky was quite cluttered with several storm cells around, with a fair amount of anvil rain. To get a better view I headed SE back out of town, and took some photos as the sky cleared a little more. On the way, I saw areas of leaf debris (indicative of hail fall) and also a few downed branches suggesting winds into the ~40kn range. Thunder was surprisingly continuous at this stage from a new cell to the west which even showed some greenage. This prompted a return trip to Nanango, only to find moderate to heavy rain with this new
storm.
Again the sky became cluttered, and without radar I decided to head towards Kingaroy for more views and the hope of storms feeding on air not cooled by the Nanango storms. At 4.30pm, an area of storms to the south moving slowly north started to look a little interesting and prompted a few photos. With heavy rain starting to fall from a storm (with the odd surprising CG) closely to the north, I went a little further towards Kingaroy onto a nice side road with views all around. The area of storms continued to creep up from the south while the storm to the north drifted away but did show some hailshafts. Off to the distant NW (west of Kingaroy) the sky was much better, with promising updrafts and new developing storms. Unfortunately they were a little too far away and I wanted to be home by about 8pm, so that wasn't an option. (A shame, because severe storms later developed on radar with insane lightning rates... but you get that!)
The southern storm area slowly moved over my area, but not before an area to the SW became quite intense for a 5-7min period, and at one point (4.40pm) I observed a very narrow ropy funnel. I've dismissed it from being anything other than a scuddy 'fake funnel' as it only lasted for a few seconds and seemed to be in an outflow area. I was too slow to for a pic at that instant, but I did take a photo, which I cropped and adjusted the contrast on. I wasn't even going to put it in this report, but I did for interests sake. The storms weakened as they moved over my location with large drops and a few small hailstones, and being about 4.50pm, I thought it was time to go back to Nanango on the way home.
As I exited the precip, a storm in the Mt Binga area came into view from the south.
As soon as I got into an area with better views, I was stoked to see such a crisp storm go up. It had been the best convection I had seen all day, and seemed isolated, in warmer surface conditions... all good for supercell development. After getting a quick update from Anthony, I continued towards Yarraman as the storm shot up very high, over 14km with a rock hard updraft. Also, off to the east of the storm, what seemed like an inflow band was starting to get organised.There was a problem however... the light windshear (and me heading towards it!) . As soon as it peaked in intensity, it started to weaken.
Video snaps: approaching the Mt Binga storm as it weakens
The full set of video snaps is here.
By the time I reached Yarraman, the updrafts had weakened considerably, and subsequent new updrafts on its western side never got close to the heights of the previous one. The base looked great at first, with a wall cloud and squally hail shafts (and great CGs), but when I finally stopped for photos on the road to Crows Nest, it had lost it completely with a weakening linear gust front and diminishing rain/hail curtain.
That signaled the end of the chase. It's amazing what slack wind shear will do to a potentially severe thunderstorm day. Sure there were some strong and severe storms around, but they all weakened quickly as they choked on their own cold outflow. Still, it was great to chase again, especially in the Brisbane Valley, where I hadn't been before.
